The Internet’s “Father Time” David L. Mills Dies at 85

January 30, 2024 by Duane Benson

Dr. Mills was one of the pioneering developers of the ARPANET, the predecessor of the internet. But his greatest legacy was the development of Network Time Protocol.

The internet’s "Father Time,” Dr. David L. Mills, passed away on January 17, 2024. In 1985, Mills developed and released the network time protocol (NTP) and continued to maintain and update it until 2008. The NTP is the fundamental protocol that synchronizes the time of systems dispersed throughout the internet.


Dr. David L. Mills

Dr. David L. Mills, Ph.D. at the University of Delaware. Image used courtesy of the University of Delaware


In addition to his invention of NTP, Mills worked on several aspects of the early internet, including the Conversational Use of Computers (CONCOMP) project and the Gateway Algorithms and Data Structures Task Force (GADS). He was also the first chairman of the Internet Architecture Task Force. He invented the first modem-based router, writing the software, which he called “Fuzzball” for a DEC LSI-11 minicomputer. Mills also assisted with the development of early protocols FTP and Ping.


From a Computer Science Education to the ARPANET

Mills was born in Oakland, California, on June 3, 1938, and was diagnosed with glaucoma at birth, eventually leaving him with limited vision in one eye. He did not let that stop him, or even slow him down, for that matter. He went on to earn two BSE degrees, an MSE degree, an MS, and a Ph.D. in computer and communication sciences. After earning his PhD, he taught computer science until 1977.

Mills undertook one of his first time-related endeavors while working at COMSAT, synchronizing the clocks of computers connected to ARPANET in 1977. He was instrumental in developing the NTP in 1985, implemented in Fuzzball and Unix. Dr. Mills returned to academia in 1986, where he spent the rest of his career. Since releasing NTP, Mills maintained full control over the NTP reference implementation until the mid-2000s when he turned it over to Harlan Stenn, his hand-picked successor. 

Mills seemed to have many of the quirks we associate with the most highly intelligent among us. In addition to nurturing NTP as though it were his child, he was an avid Ham radio operator, photographer, and hiker.


Dr. Mills’ Ham radio setup
Dr. Mills’ Ham radio setup. Image used courtesy of the University of Delaware

Mills was known for his strict concern over language rules. Like Shakespeare, he also made personal contributions to the English language, with offerings such as: “truechimers” and “falsetickers.” His propensity to, as he wrote on his University page, “twitch the English language” led friends and colleagues to coin the term “Millsspeak.”


What Is the Network Time Protocol (NTP)?

The Network Time Protocol (NTP) is a method of keeping computer clocks synchronized across a packet-switched network, where the latency between systems is unknown and unpredictable. NTP is designed to keep computers synchronized within a few milliseconds to the reference clock, Coordinated Universal Time (UTC).

In practice, it keeps systems on the public internet synced to within a few tens of milliseconds and systems on local networks within a single millisecond or less. It can operate in either client-server or peer-to-peer modes and considers multiple layers between systems and the time reference. The nodes send timestamps back and forth using user datagram protocol (UDP) on port 123.

NTP multi-tired compare and select
NTP multi-tired compare and select. Image used courtesy of Wikimedia Commons/Benjamin D. Esham (Public domain)

The heart of NTP is the ”intersection algorithm,” a method for comparing multiple time sources and determining the most likely to be the correct source. NTP then makes this information available to clients or peers and maintains consistency despite the varying latency over public networks.

In operation, a client will poll one or more NTP servers and receive a timestamp. The client must determine the round-trip delay between it and the designated server and then calculate a positive or negative time offset from its own clock. One of the limitations of this approach is that it assumes an equal delay for the outgoing request and the incoming response. In practice, the two delays are often close but rarely equal. Research is currently underway to find a solution to this issue and deliver even more accurate time.


Time: It’s All Relative

According to the doctor from the long-running BBC TV series “Dr. Who,” time is "a big ball of wibbly wobbly, timey wimpy stuff." But to those of us who exist on the internet as much as we do in the physical realm, time is a mission-critical reference. Mills knew exactly how critical that time reference is and made it his life’s work.

He stated the following in the preface of his book, “Computer Network Time Synchronization: the Network Time Protocol on Earth and in Space, Second Edition”:

“Carefully coordinated, reliable and accurate time is vital for traffic control in the air and on the ground, buying and selling things and TV network programming. Even worse, ill-gotten time might cause DNS caches to expire and the entire Internet to implode on the root servers … Critical data files might expire before they are created, and an electronic message might arrive before it was sent. “

To Mills, time was an imperative and an obligation. He once said that he paid so much attention to network time because no one else would. This belief gave him a sense of self-imposed responsibility and personal fiefdom over internet time.

For his contribution to network protocol and timekeeping, Mills was inducted as a fellow of the Association for Computing Machinery in 1999 and the Institute of Electrical and Electronics Engineers (IEEE) in 2002. In 2008, he was elected a member of the National Academy of Engineering (NAE). He was awarded the IEEE Internet Award in 2013 for his critical contributions to time synchronization development for the internet.